Name
ARB_copy_image
Name Strings
GL_ARB_copy_image
Contact
Michael Gold, NVIDIA Corporation (gold 'at' nvidia.com)
Graham Sellers, AMD (graham.sellers 'at' amd.com)
Contributors
Jeff Bolz, NVIDIA Corporation (jbolz 'at' nvidia.com)
James Jones, NVIDIA Corporation (jajones 'at' nvidia.com)
Joe Kain, NVIDIA Corporation (jkain 'at' nvidia.com)
Benjamin Morris, NVIDIA Corporation (bmorris 'at' nvidia.com)
Michael Morrison, NVIDIA Corporation (mmorrison 'at' nvidia.com)
Aaron Plattner, NVIDIA Corporation (aplattner 'at' nvidia.com)
Mathias Schott, NVIDIA Corporation (mschott 'at' nvidia.com)
Thomas Volk, NVIDIA Corporation (tvolk 'at' nvidia.com)
Eric Werness, NVIDIA Corporation (ewerness 'at' nvidia.com)
Daniel Koch, TransGaming Inc. (daniel 'at' transgaming.com)
Notice
Copyright (c) 2012-2013 The Khronos Group Inc. Copyright terms at
http://www.khronos.org/registry/speccopyright.html
Status
Complete.
Approved by the ARB on 2012/06/12.
Version
Last Modified Date: May 10, 2012
Revision: 3
Number
ARB Extension #123
Dependencies
OpenGL 1.1 is required.
The extension is written against the OpenGL 4.2 (Core Profile) Specification.
This extension interacts with OpenGL 4.3 and ARB_texture_view.
This extension interacts with the Compatibility Profile.
This extension interacts with EXT_texture_compression_s3tc.
This extension interacts with OpenGL 3.0 and ARB_texture_compression_rgtc.
This extension interacts with OpenGL 4.2 and ARB_texture_compression_bptc.
Overview
This extension enables efficient image data transfer between image
objects (i.e. textures and renderbuffers) without the need to bind
the objects or otherwise configure the rendering pipeline.
This is accomplised by adding a new entry-point CopyImageSubData,
which takes a named source and destination.
CopyImageSubData does not perform general-purpose conversions
such as scaling, resizing, blending, color-space, or format
conversions. It should be considered to operate in a manner
similar to a CPU memcpy, but using the GPU for the copy.
CopyImageSubData supports copies between images with different
internal formats, if the formats are compatible for TextureViews.
CopyImageSubData also supports copying between compressed and
uncompressed images if the compressed block / uncompressed texel
sizes are the same.
New Procedures and Functions
void CopyImageSubData(
uint srcName, enum srcTarget, int srcLevel,
int srcX, int srcY, int srcZ,
uint dstName, enum dstTarget, int dstLevel,
int dstX, int dstY, int dstZ,
sizei srcWidth, sizei srcHeight, sizei srcDepth);
New Tokens
None
Additions to Chapter 4 of the OpenGL 4.2 (Core Profile) Specification (Per-Fragment
Operations and the Frame Buffer)
Append to section 4.3.2 (Copying Pixels):
The function
void CopyImageSubData(
uint srcName, enum srcTarget, int srcLevel,
int srcX, int srcY, int srcZ,
uint dstName, enum dstTarget, int dstLevel,
int dstX, int dstY, int dstZ,
sizei srcWidth, sizei srcHeight, sizei srcDepth);
may be used to copy a region of texel data between two image
objects. An image object may be either a texture or a
renderbuffer.
CopyImageSubData does not perform general-purpose conversions
such as scaling, resizing, blending, color-space, or format
conversions. It should be considered to operate in a manner
similar to a CPU memcpy. CopyImageSubData can copy between
images with different internal formats, provided
the formats are compatible.
CopyImageSubData also allows copying between certain
types of compressed and uncompressed internal formats as detailed
in Table 4.X.1. This copy does not perform on-the-fly compression
or decompression. When copying from an uncompressed internal format
to a compressed internal format, each texel of uncompressed data
becomes a single block of compressed data. When copying from a
compressed internal format to an uncompressed internal format,
a block of compressed data becomes a single texel of uncompressed
data. The texel size of the uncompressed format must be the same
size the block size of the compressed formats. Thus it is permitted
to copy between a 128-bit uncompressed format and a compressed
format which uses 8-bit 4x4 blocks, or between a 64-bit uncompressed
format and a compressed format which uses 4-bit 4x4 blocks.
INVALID_OPERATION is generated if the texel size of
the uncompressed image is not equal to the block size of the
compressed image.
The source object is identified by and .
Similarly the destination object is identified by and
. The interpretation of the name depends on the value
of the corresponding target parameter. If the target parameter is
RENDERBUFFER, the name is interpreted as the name of a
renderbuffer object. If the target parameter is a texture target,
the name is interpreted as a texture object. All non-proxy
texture targets are accepted, with the exception of TEXTURE_BUFFER
and the cubemap face selectors described in table 3.17.
INVALID_ENUM is generated if either target is not RENDERBUFFER
or a valid non-proxy texture target, or is TEXTURE_BUFFER, or is one
of the cubemap face selectors described in table 3.17, or if the
target does not match the type of the object. INVALID_OPERATION
is generated if either object is a texture and the texture is
not complete (as defined in section 3.9.14), if the source and
destination internal formats are not compatible (see below),
or if the number of samples do not match.
INVALID_VALUE is generated if either name does not correspond to a
valid renderbuffer or texture object according to the corresponding
target parameter.
and identify the source and destination
level of detail. For textures, this must be a valid level of
detail in the texture object. For renderbuffers, this value must
be zero. INVALID_VALUE is generated if the specified level is not
a valid level for the image.
, , and specify the lower left texel
coordinates of a -wide by -high by
-deep rectangular subregion of the source texel array.
(Compatibility Only: Negative values
of , , and correspond to the coordinates of
border texels, addressed as in figure 3.10.) Similarly, ,
and specify the coordinates of a subregion of the
destination texel array. The source and destination subregions
must be contained entirely within the specified level of the
corresponding image objects.
The dimensions are always specified in texels, even for compressed
texture formats. But it should be noted that if only one of the
source and destination textures is compressed then the number of
texels touched in the compressed image will be a factor of the
block size larger than in the uncompressed image.
INVALID_VALUE is generated if the
dimensions of the either subregion exceeds the boundaries of the
corresponding image object, or if the image format is compressed
and the dimensions of the subregion fail to meet the alignment
constraints of the format.
Slices of a TEXTURE_1D_ARRAY, TEXTURE_2D_ARRAY, TEXTURE_CUBE_MAP_ARRAY
TEXTURE_3D and faces of TEXTURE_CUBE_MAP are all compatible provided
they share a compatible internal format, and multiple slices or faces
may be copied between these objects with a single call by specifying the
starting slice with and , and the number of slices to
be copied with . Cubemap textures always have six faces
which are selected by a zero-based face index, according to the
order specified in table 3.17.
For the purposes of CopyImageSubData, two internal formats
are considered compatible if any of the following conditions are
met:
* the formats are the same,
* the formats are considered compatible according to the
compatibility rules used for texture views as defined in
section 3.9.X. In particular, if both internal formats are listed
in the same entry of Table 3.X.2, they are considered compatible, or
* one format is compressed and the other is uncompressed and
Table 4.X.1 lists the two formats in the same row.
If the formats are not compatible INVALID_OPERATION is generated.
------------------------------------------------------------------------
| Texel / | Uncompressed | |
| Block | internal format | Compressed internal format |
| size | | |
------------------------------------------------------------------------
| 128-bit | RGBA32UI, | COMPRESSED_RGBA_S3TC_DXT3_EXT, |
| | RGBA32I, | COMPRESSED_SRGB_ALPHA_S3TC_DXT3_EXT,|
| | RGBA32F | COMPRESSED_RGBA_S3TC_DXT5_EXT, |
| | | COMPRESSED_SRGB_ALPHA_S3TC_DXT5_EXT,|
| | | COMPRESSED_RG_RGTC2, |
| | | COMPRESSED_SIGNED_RG_RGTC2, |
| | | COMPRESSED_RGBA_BPTC_UNORM, |
| | | COMPRESSED_SRGB_ALPHA_BPTC_UNORM, |
| | | COMPRESSED_RGB_BPTC_SIGNED_FLOAT, |
| | | COMPRESSED_RGB_BPTC_UNSIGNED_FLOAT |
------------------------------------------------------------------------
| 64-bit | RGBA16F, RG32F, | COMPRESSED_RGB_S3TC_DXT1_EXT, |
| | RGBA16UI, RG32UI, | COMPRESSED_SRGB_S3TC_DXT1_EXT, |
| | RGBA16I, RG32I, | COMPRESSED_RGBA_S3TC_DXT1_EXT, |
| | RGBA16, RGBA16_SNORM | COMPRESSED_SRGB_ALPHA_S3TC_DXT1_EXT,|
| | | COMPRESSED_RED_RGTC1, |
| | | COMPRESSED_SIGNED_RED_RGTC1 |
------------------------------------------------------------------------
Table 4.X.1: Compatible internal formats for copying between
compressed and uncompressed internal formats with CopyImageSubData.
Formats in the same row can be copied between each other.
Dependencies on OpenGL 4.3 and ARB_texture_view:
If OpenGL 4.3 or later and ARB_texture_view are not supported,
any references to view-compatible image formats should be removed.
Dependencies on the Compatibility Profile:
If the Compatibility Profile is not supported, remove any
references to negative values for the source dimensions and
to border texels.
Dependencies on EXT_texture_compression_s3tc:
If EXT_texture_compression_s3tc is not supported, remove any
references to S3TC compressed texture formats.
Dependencies on OpenGL 3.0 and ARB_texture_compression_rgtc:
If OpenGL 3.0 or later, and ARB_texture_compression_rgtc is not
supported, remove any references to the RGTC compressed texture
formats.
Dependencies on OpenGL 4.2 and ARB_texture_compression_bptc:
If OpenGL 4.2 or later, and ARB_texture_compression_bptc is not
supported, remove any references to the PBTC compressed texture
formats.
Errors
CopyImageSubData may fail with any of the following errors:
INVALID_ENUM is generated
* if either or
- is not RENDERBUFFER or a valid non-proxy texture target
- is TEXTURE_BUFFER, or
- is one of the cubemap face selectors described in table 3.17,
* if the target does not match the type of the object.
INVALID_OPERATION is generated
* if either object is a texture and the texture is not complete,
* if the source and destination formats are not compatible,
* if the source and destination number of samples do not match,
* if one image is compressed and the other is uncompressed and the
block size of compressed image is not equal to the texel size
of the compressed image.
INVALID_VALUE is generated
* if either or does not correspond to a valid
renderbuffer or texture object according to the corresponding
target parameter, or
* if the specified level is not a valid level for the image, or
* if the dimensions of the either subregion exceeds the boundaries
of the corresponding image object, or
* if the image format is compressed and the dimensions of the
subregion fail to meet the alignment constraints of the format.
Sample Code
TBD
Issues
1) Should there be a single function for all image types, or
"per-dimensional" functions?
RESOLVED: A single function can support all image types. Not only are
per-dimensional functions an unnecessary convenience, they also
restrict some of the flexibility offered by this extension,
e.g. copying a slice of data between a 2D and a 3D image.
2) Should the extension support "deep copies", i.e. multiple slices of
a 3D texture, a 2D array texture, or a cubemap?
RESOLVED: Yes, there may be performance advantages in copying a multiple
slices in a single call.
3) Should renderbuffers be supported by the same function as textures?
RESOLVED: Yes, there is no fundamental difference between the two object
classes, and allowing them to be used interchangeably has the
advantage of allowing data transfers between them.
4) Is the "target" parameter necessary?
RESOLVED: Yes, given the current object model and texture API, there are
two obvious applications of the target parameter:
1) Allows the selection of a single cubemap face.
2) Differentiate between TEXTURE and RENDERBUFFER targets.
5) Should the target TEXTURE_CUBE_MAP be supported, and with what
behavior?
RESOLVED: Given the resolution of issue 7, this is moot. The
TEXTURE_CUBE_MAP token is the only way to access a cubemap.
6) Should the "extra" parameters for a given dimension be ignored, or
should there be required values?
Resolved.
All parameters are required to have sensible values, for the
simple reason that future extensions may give meaning to these
values. For dimensions which are currently superfluous, the
offset must be zero and the size must be one, e.g. if the target
is TEXTURE_2D, z must be 0 and depth must be 1.
7) Should the per-face cubemap targets be accepted at all? Why not
use Z as the selector?
Resolved.
The existing per-face targets effectively define the face order:
face_index = face_target - TEXTURE_CUBE_MAP_POSITIVE_X;
Therefore it makes sense to generalize a cubemap as an array of
size 6, and use the Z parameter to select the face(s).
8) How is this extension different from NV_copy_image?
RESOLVED: This extension does not include the WGL/GLX windowing-
layer copy functions. This extension adds the ability to copy
between images which have different formats where the formats
are compatible for texture views. This extension adds the ability
to copy between uncompressed and compressed images if the texel
and block sizes are the same.
9) Please explain copying between compressed and uncompressed images.
Is the copy doing compression/decompression on the fly?
DISCUSSION. The CopyImageSubData does NOT provide any on-the-fly
compression, decompression, or even any format conversions.
Instead, it provides the ability for an application to implement
it's own compressor in a shader by constructing the blocks and
writing them out as texels and then copying them to a compressed
texture so that it can in turn be used for sampling.
(10) Is copying from/to images with ETC2/EAC compressed texture formats
defined?
RESOLVED: Only when the source and destination formats are identical,
because texture view classes for ETC2/EAC are not defined (see issue 13
of the ARB_texture_view specification).
Revision History
Rev. Date Author Changes
---- -------- -------- -----------------------------------------
1 04/26/2012 gsellers Initial revision based on NV_copy_image.
2 05/08/2012 dgkoch Update some references for 4.2 spec
Allow copies between view-compatible images.
Allow copies between compressed/uncompressed images.
Clarify errors, updated overview.
3 05/10/2012 dgkoch Clarify dimensions refer to texels in the src image.
Re-order/reflow text to make it read better.
Add mention of TEXTURE_CUBE_MAP_ARRAY.
4 10/08/2013 Jon Leech Add issue 10 discussing why copying
involving conversions between ETC2/EAC
compressed formats is not supported (Bug
11011).